Orthodontic appliances are used for applying corrective forces to misaligned teeth. The appliances generally include brackets, which are mounted on the teeth, arch wires slidingly mounted in the brackets for applying forces and for guiding movement, and elastics or other force transmitting members connected to the brackets for applying additional corrective forces to the teeth.
Conventional brackets generally include a base portion, which abuts the tooth surface, an outer portion, which has a slot formed therein for receiving an arch wire, and hook members, on which elastics, ligatures or other force transmitting members can be attached.
A typical single bracket has an outer portion comprising a single vertically-oriented bar with a small horizontal slot formed therein for receiving the arch wire. Twin brackets have an outer portion comprising a pair of parallel, vertically-oriented bars that are spaced apart with a slot cut in each bar to receive the arch wire. Other brackets of various shapes are known including a bracket having an outer portion with a generally "Y" shape with an arch wire slot formed therein.
Single wing brackets that are narrow in width or have small slots create smaller moments from the contact between the arch wire and the bracket, thereby making torque, tip and rotational control difficult during tooth movement. Also, such brackets frequently cause entrapment of food and are hygienically not the most desirable.
Many known brackets including typically twin type brackets have large widths or long arch wire slots to increase the magnitude of moments created by contact between the arch wire and the slot. By increasing the moments, tip, torque and rotational control of the teeth is enhanced during tooth movement. However, one disadvantage to having such long slots or large bracket widths is that it reduces the inter-bracket distance or the distance between brackets on adjacent teeth. Consequently, the span of the arch wire between the brackets is small, which reduces the flexibility of the wire and makes it difficult to control forces exerted by the wire.
Another problem with brackets having long arch wire slots is that there may be substantial undesirable friction between the arch wire and the bracket during tooth movement. Additionally, brackets having large widths are difficult to place and orient on the tooth.
Accordingly, one object of this invention is to provide a bracket that has excellent rotational, tip and torque control, yet provides sufficiently large inter-bracket distances to enable effective use of arch wires and to reduce friction between the bracket and the arch wire. Another object of this invention to provide a bracket that is easy to orient and position on the tooth surface.